Protein phosphatases 1 and 2A and their naturally occurring inhibitors: current topics in smooth muscle physiology and chemical biology

Abstract

Protein phosphatases 1 and 2A (PP1 and PP2A) are the most ubiquitous and abundant serine/threonine phosphatases in eukaryotic cells. They play fundamental roles in the regulation of various cellular functions. This review focuses on recent advances in the functional studies of these enzymes in the field of smooth muscle physiology. Many naturally occurring protein phosphatase inhibitors with different relative PP1/PP2A affinities have been discovered and are widely used as powerful research tools. Current topics in the chemical biology of PP1/PP2A inhibitors are introduced and discussed, highlighting the identification of the gene cluster responsible for the biosynthesis of calyculin A in a symbiont microorganism of a marine sponge.

The Cell Cycle Checkpoint System MAST(L)-ENSA/ARPP19-PP2A is Targeted by cAMP/PKA and cGMP/PKG in Anucleate Human Platelets

“…This Ser/Thr-phosphatase assay was optimized for PP2A by selective assay conditions including a specific buffer, selective peptide substrate and appropriately desalted recombinant proteins and cell lysates ( Figure 5). This measured phosphatase activity was potently inhibited by OA (concentrations of 1 nM and even below) and by fostriecin (0.3-3.0 nM) (Figure 5a), in agreement with the reported IC 50 of 0.1-0.3 nM OA or of 1-3 nM fostriecin for PP2A inhibition, respectively [56,62]. In contrast, the PP1 inhibitor tautomycetin (reported IC 50 for PP1~0.5 nM, IC50 50 for PP2A~62 nM) [56,63] had inhibitory effects on the measured phosphatase activity only at concentrations of 50 nM and higher.…”

“…This measured phosphatase activity was potently inhibited by OA (concentrations of 1 nM and even below) and by fostriecin (0.3-3.0 nM) (Figure 5a), in agreement with the reported IC 50 of 0.1-0.3 nM OA or of 1-3 nM fostriecin for PP2A inhibition, respectively [56,62]. In contrast, the PP1 inhibitor tautomycetin (reported IC 50 for PP1~0.5 nM, IC50 50 for PP2A~62 nM) [56,63] had inhibitory effects on the measured phosphatase activity only at concentrations of 50 nM and higher. These data established the conditions to study and compare the effects of known (low dose OA) and putative inhibitors of PP2A such as S67/S62-phosphorylated ENSA/ARPP19.…”

“…The availability of recombinant ENSA and ARPP19 in various phospho-variants allowed the analysis of their effects on platelet serine/threonine protein phosphatases. Although the general importance of serine/threonine protein phosphatase including PP2A as signalling opponent of serine/ threonine protein kinases has been recognized [25,26,56], the diversity and distinct regulatory mechanisms of serine/threonine protein phosphatases were only recently discovered, also supported by the complete description of the human protein kinome [57] and protein phosphatome [58]. With this background and our quantitative human platelet proteome data [34] it was possible to compile an overview of most serine/threonine protein phosphatases present in human platelets which include three catalytic subunits of PP1 and two catalytic subunits (α,β) of PP2A (Table S1).…”

“…A 30 min incubation of intact human platelets with 200 nM OA strongly increased the phosphorylation of VASP (at S157 and S239), Akt (at T308 and S473), p38 (at T180/Y182) and p44/42 MAPK (Erk 1/2) (at T202/Y204) with initial effects observed within 10 min (Figure 7; Figure S6) after OA addition. It needs to be considered that 200 nM OA used here with intact human platelets is relatively high compared to the PP2A inhibition by OA in cell free lysates (Ki 0.032 nM) and may affect PP1 (inhibition by OA in cell free lysates, Ki 150 nM) [56]. However, the conditions with intact cells (here intact platelets) are determined by additional factors.…”

Identification of peptides interfering the lrrk2/pp1 interaction

“…Serine/threonine protein phosphatases 1 and 2A (PP1 and PP2A) are the most ubiquitous and abundant serine/threonine phosphatases in eukaryotic cells and they are implicated in the regulation of various essential cellular functions 1,2 . PP1 is a single-domain hub protein with nearly 200 validated interactors in vertebrates.…”